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A267873
Number of ON (black) cells in the n-th iteration of the "Rule 235" elementary cellular automaton starting with a single ON (black) cell.
1
1, 1, 4, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125
OFFSET
0,3
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
FORMULA
Conjectures from Colin Barker, Jan 22 2016 and Apr 20 2019: (Start)
a(n) = 2*a(n-1)-a(n-2) for n>2.
G.f.: (1-x+3*x^2-x^4) / (1-x)^2.
(End)
MATHEMATICA
rule=235; rows=20; ca=CellularAutomaton[rule, {{1}, 0}, rows-1, {All, All}]; (* Start with single black cell *) catri=Table[Take[ca[[k]], {rows-k+1, rows+k-1}], {k, 1, rows}]; (* Truncated list of each row *) Table[Total[catri[[k]]], {k, 1, rows}] (* Number of Black cells in stage n *)
CROSSREFS
Cf. A267869.
Sequence in context: A272454 A207017 A174724 * A310943 A310944 A024704
KEYWORD
nonn,easy
AUTHOR
Robert Price, Jan 21 2016
STATUS
approved